src/librustc_data_structures/bitvec.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use std::iter::FromIterator;
  12
  13 /// A very simple BitVector type.
  14 #[derive(Clone, Debug, PartialEq)]
  15 pub struct BitVector {
  16     data: Vec<u64>,
  17 }
  18
  19 impl BitVector {
  20     #[inline]
  21     pub fn new(num_bits: usize) -> BitVector {
  22         let num_words = u64s(num_bits);
  23         BitVector { data: vec![0; num_words] }
  24     }
  25
  26     #[inline]
  27     pub fn clear(&mut self) {
  28         for p in &mut self.data {
  29             *p = 0;
  30         }
  31     }
  32
  33     pub fn count(&self) -> usize {
  34         self.data.iter().map(|e| e.count_ones() as usize).sum()
  35     }
  36
  37     #[inline]
  38     pub fn contains(&self, bit: usize) -> bool {
  39         let (word, mask) = word_mask(bit);
  40         (self.data[word] & mask) != 0
  41     }
  42
  43     /// Returns true if the bit has changed.
  44     #[inline]
  45     pub fn insert(&mut self, bit: usize) -> bool {
  46         let (word, mask) = word_mask(bit);
  47         let data = &mut self.data[word];
  48         let value = *data;
  49         let new_value = value | mask;
  50         *data = new_value;
  51         new_value != value
  52     }
  53
  54     #[inline]
  55     pub fn insert_all(&mut self, all: &BitVector) -> bool {
  56         assert!(self.data.len() == all.data.len());
  57         let mut changed = false;
  58         for (i, j) in self.data.iter_mut().zip(&all.data) {
  59             let value = *i;
  60             *i = value | *j;
  61             if value != *i {
  62                 changed = true;
  63             }
  64         }
  65         changed
  66     }
  67
  68     #[inline]
  69     pub fn grow(&mut self, num_bits: usize) {
  70         let num_words = u64s(num_bits);
  71         if self.data.len() < num_words {
  72             self.data.resize(num_words, 0)
  73         }
  74     }
  75
  76     /// Iterates over indexes of set bits in a sorted order
  77     #[inline]
  78     pub fn iter<'a>(&'a self) -> BitVectorIter<'a> {
  79         BitVectorIter {
  80             iter: self.data.iter(),
  81             current: 0,
  82             idx: 0,
  83         }
  84     }
  85 }
  86
  87 pub struct BitVectorIter<'a> {
  88     iter: ::std::slice::Iter<'a, u64>,
  89     current: u64,
  90     idx: usize,
  91 }
  92
  93 impl<'a> Iterator for BitVectorIter<'a> {
  94     type Item = usize;
  95     fn next(&mut self) -> Option<usize> {
  96         while self.current == 0 {
  97             self.current = if let Some(&i) = self.iter.next() {
  98                 if i == 0 {
  99                     self.idx += 64;
 100                     continue;
 101                 } else {
 102                     self.idx = u64s(self.idx) * 64;
 103                     i
 104                 }
 105             } else {
 106                 return None;
 107             }
 108         }
 109         let offset = self.current.trailing_zeros() as usize;
 110         self.current >>= offset;
 111         self.current >>= 1; // shift otherwise overflows for 0b1000_0000_…_0000
 112         self.idx += offset + 1;
 113         return Some(self.idx - 1);
 114     }
 115 }
 116
 117 impl FromIterator<bool> for BitVector {
 118     fn from_iter<I>(iter: I) -> BitVector where I: IntoIterator<Item=bool> {
 119         let iter = iter.into_iter();
 120         let (len, _) = iter.size_hint();
 121         // Make the minimum length for the bitvector 64 bits since that's
 122         // the smallest non-zero size anyway.
 123         let len = if len < 64 { 64 } else { len };
 124         let mut bv = BitVector::new(len);
 125         for (idx, val) in iter.enumerate() {
 126             if idx > len {
 127                 bv.grow(idx);
 128             }
 129             if val {
 130                 bv.insert(idx);
 131             }
 132         }
 133
 134         bv
 135     }
 136 }
 137
 138 /// A "bit matrix" is basically a matrix of booleans represented as
 139 /// one gigantic bitvector. In other words, it is as if you have
 140 /// `rows` bitvectors, each of length `columns`.
 141 #[derive(Clone)]
 142 pub struct BitMatrix {
 143     columns: usize,
 144     vector: Vec<u64>,
 145 }
 146
 147 impl BitMatrix {
 148     // Create a new `rows x columns` matrix, initially empty.
 149     pub fn new(rows: usize, columns: usize) -> BitMatrix {
 150         // For every element, we need one bit for every other
 151         // element. Round up to an even number of u64s.
 152         let u64s_per_row = u64s(columns);
 153         BitMatrix {
 154             columns,
 155             vector: vec![0; rows * u64s_per_row],
 156         }
 157     }
 158
 159     /// The range of bits for a given row.
 160     fn range(&self, row: usize) -> (usize, usize) {
 161         let u64s_per_row = u64s(self.columns);
 162         let start = row * u64s_per_row;
 163         (start, start + u64s_per_row)
 164     }
 165
 166     pub fn add(&mut self, source: usize, target: usize) -> bool {
 167         let (start, _) = self.range(source);
 168         let (word, mask) = word_mask(target);
 169         let vector = &mut self.vector[..];
 170         let v1 = vector[start + word];
 171         let v2 = v1 | mask;
 172         vector[start + word] = v2;
 173         v1 != v2
 174     }
 175
 176     /// Do the bits from `source` contain `target`?
 177     ///
 178     /// Put another way, if the matrix represents (transitive)
 179     /// reachability, can `source` reach `target`?
 180     pub fn contains(&self, source: usize, target: usize) -> bool {
 181         let (start, _) = self.range(source);
 182         let (word, mask) = word_mask(target);
 183         (self.vector[start + word] & mask) != 0
 184     }
 185
 186     /// Returns those indices that are reachable from both `a` and
 187     /// `b`. This is an O(n) operation where `n` is the number of
 188     /// elements (somewhat independent from the actual size of the
 189     /// intersection, in particular).
 190     pub fn intersection(&self, a: usize, b: usize) -> Vec<usize> {
 191         let (a_start, a_end) = self.range(a);
 192         let (b_start, b_end) = self.range(b);
 193         let mut result = Vec::with_capacity(self.columns);
 194         for (base, (i, j)) in (a_start..a_end).zip(b_start..b_end).enumerate() {
 195             let mut v = self.vector[i] & self.vector[j];
 196             for bit in 0..64 {
 197                 if v == 0 {
 198                     break;
 199                 }
 200                 if v & 0x1 != 0 {
 201                     result.push(base * 64 + bit);
 202                 }
 203                 v >>= 1;
 204             }
 205         }
 206         result
 207     }
 208
 209     /// Add the bits from `read` to the bits from `write`,
 210     /// return true if anything changed.
 211     ///
 212     /// This is used when computing transitive reachability because if
 213     /// you have an edge `write -> read`, because in that case
 214     /// `write` can reach everything that `read` can (and
 215     /// potentially more).
 216     pub fn merge(&mut self, read: usize, write: usize) -> bool {
 217         let (read_start, read_end) = self.range(read);
 218         let (write_start, write_end) = self.range(write);
 219         let vector = &mut self.vector[..];
 220         let mut changed = false;
 221         for (read_index, write_index) in (read_start..read_end).zip(write_start..write_end) {
 222             let v1 = vector[write_index];
 223             let v2 = v1 | vector[read_index];
 224             vector[write_index] = v2;
 225             changed = changed | (v1 != v2);
 226         }
 227         changed
 228     }
 229
 230     pub fn iter<'a>(&'a self, row: usize) -> BitVectorIter<'a> {
 231         let (start, end) = self.range(row);
 232         BitVectorIter {
 233             iter: self.vector[start..end].iter(),
 234             current: 0,
 235             idx: 0,
 236         }
 237     }
 238 }
 239
 240 #[inline]
 241 fn u64s(elements: usize) -> usize {
 242     (elements + 63) / 64
 243 }
 244
 245 #[inline]
 246 fn word_mask(index: usize) -> (usize, u64) {
 247     let word = index / 64;
 248     let mask = 1 << (index % 64);
 249     (word, mask)
 250 }
 251
 252 #[test]
 253 fn bitvec_iter_works() {
 254     let mut bitvec = BitVector::new(100);
 255     bitvec.insert(1);
 256     bitvec.insert(10);
 257     bitvec.insert(19);
 258     bitvec.insert(62);
 259     bitvec.insert(63);
 260     bitvec.insert(64);
 261     bitvec.insert(65);
 262     bitvec.insert(66);
 263     bitvec.insert(99);
 264     assert_eq!(bitvec.iter().collect::<Vec<_>>(),
 265                [1, 10, 19, 62, 63, 64, 65, 66, 99]);
 266 }
 267
 268
 269 #[test]
 270 fn bitvec_iter_works_2() {
 271     let mut bitvec = BitVector::new(319);
 272     bitvec.insert(0);
 273     bitvec.insert(127);
 274     bitvec.insert(191);
 275     bitvec.insert(255);
 276     bitvec.insert(319);
 277     assert_eq!(bitvec.iter().collect::<Vec<_>>(), [0, 127, 191, 255, 319]);
 278 }
 279
 280 #[test]
 281 fn union_two_vecs() {
 282     let mut vec1 = BitVector::new(65);
 283     let mut vec2 = BitVector::new(65);
 284     assert!(vec1.insert(3));
 285     assert!(!vec1.insert(3));
 286     assert!(vec2.insert(5));
 287     assert!(vec2.insert(64));
 288     assert!(vec1.insert_all(&vec2));
 289     assert!(!vec1.insert_all(&vec2));
 290     assert!(vec1.contains(3));
 291     assert!(!vec1.contains(4));
 292     assert!(vec1.contains(5));
 293     assert!(!vec1.contains(63));
 294     assert!(vec1.contains(64));
 295 }
 296
 297 #[test]
 298 fn grow() {
 299     let mut vec1 = BitVector::new(65);
 300     for index in 0 .. 65 {
 301         assert!(vec1.insert(index));
 302         assert!(!vec1.insert(index));
 303     }
 304     vec1.grow(128);
 305
 306     // Check if the bits set before growing are still set
 307     for index in 0 .. 65 {
 308         assert!(vec1.contains(index));
 309     }
 310
 311     // Check if the new bits are all un-set
 312     for index in 65 .. 128 {
 313         assert!(!vec1.contains(index));
 314     }
 315
 316     // Check that we can set all new bits without running out of bounds
 317     for index in 65 .. 128 {
 318         assert!(vec1.insert(index));
 319         assert!(!vec1.insert(index));
 320     }
 321 }
 322
 323 #[test]
 324 fn matrix_intersection() {
 325     let mut vec1 = BitMatrix::new(200, 200);
 326
 327     // (*) Elements reachable from both 2 and 65.
 328
 329     vec1.add(2, 3);
 330     vec1.add(2, 6);
 331     vec1.add(2, 10); // (*)
 332     vec1.add(2, 64); // (*)
 333     vec1.add(2, 65);
 334     vec1.add(2, 130);
 335     vec1.add(2, 160); // (*)
 336
 337     vec1.add(64, 133);
 338
 339     vec1.add(65, 2);
 340     vec1.add(65, 8);
 341     vec1.add(65, 10); // (*)
 342     vec1.add(65, 64); // (*)
 343     vec1.add(65, 68);
 344     vec1.add(65, 133);
 345     vec1.add(65, 160); // (*)
 346
 347     let intersection = vec1.intersection(2, 64);
 348     assert!(intersection.is_empty());
 349
 350     let intersection = vec1.intersection(2, 65);
 351     assert_eq!(intersection, &[10, 64, 160]);
 352 }
 353
 354 #[test]
 355 fn matrix_iter() {
 356     let mut matrix = BitMatrix::new(64, 100);
 357     matrix.add(3, 22);
 358     matrix.add(3, 75);
 359     matrix.add(2, 99);
 360     matrix.add(4, 0);
 361     matrix.merge(3, 5);
 362
 363     let expected = [99];
 364     let mut iter = expected.iter();
 365     for i in matrix.iter(2) {
 366         let j = *iter.next().unwrap();
 367         assert_eq!(i, j);
 368     }
 369     assert!(iter.next().is_none());
 370
 371     let expected = [22, 75];
 372     let mut iter = expected.iter();
 373     for i in matrix.iter(3) {
 374         let j = *iter.next().unwrap();
 375         assert_eq!(i, j);
 376     }
 377     assert!(iter.next().is_none());
 378
 379     let expected = [0];
 380     let mut iter = expected.iter();
 381     for i in matrix.iter(4) {
 382         let j = *iter.next().unwrap();
 383         assert_eq!(i, j);
 384     }
 385     assert!(iter.next().is_none());
 386
 387     let expected = [22, 75];
 388     let mut iter = expected.iter();
 389     for i in matrix.iter(5) {
 390         let j = *iter.next().unwrap();
 391         assert_eq!(i, j);
 392     }
 393     assert!(iter.next().is_none());
 394 }